The Effect of Microstructure on the Galvanostatic Discharge of Graphite Anode Electrodes in LiCoO2-Based Rocking-Chair Rechargeable Batteries

By starting from experimentally determined cross sections of rechargeable lithium-ion batteries, the effect of microstructure on the galvanostatic discharge of a LiCoO2 vertical bar LiC6 cell was numerically modeled. Results demonstrate that when small graphite particles are part of a population with large particle sizes, diminished macroscopic power densities develop and limit the response of the entirety of the cell. Small particle-size populations electrochemically interact with large particle-size populations and lead to a macroscopic capacity loss, compared to cells with uniform particle size. Such capacity loss is a result of the lithium exchange between small and large anode particle-size populations, instead of the lithium exchange between electrode particles of opposite polarity. The analysis suggests that graphite particles of size smaller than the average value dominate the macroscopic electrical response of the device, for the induced localized lithium depletion leads to an increase in the polarization losses of the anode. Lithium depletion in the anode starts in the small particles, is followed by particles of complex morphology and rough surfaces, and continues with the depletion of large particles embedded in a fast diffusion environment. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3216000] All rights reserved.